1. Field of the Invention
This invention relates to polypeptides analogous to human superoxide dismutase, which have a sequence of at least 153 amino acids and represented by the following general formula (I): ##STR2## wherein X.sub.1 means a hydrogen atom, acetyl group or amino acid residue, X.sub.2 and X.sub.3 are either the same or different and mean individually an amino acid residue, and when X.sub.2 stands for Cys, X.sub.3 denotes an amino acid residue other than Cys, and their preparation process, as well as their copper- and/or zinc-coordinated dimers represented by the following formula (II): EQU 2 [polypeptide (I).].Y.sub.1 Cu.sup.2+.Y.sub.2 Zn.sup.2+ (II)
wherein Y.sub.1 and Y.sub.2 stand individually for an integer of 0-4 and Y.sub.1 +Y.sub.2 is 2 or 4.
2. Description of the Prior Art
Superoxide dismutase (hereinafter abbreviated as "SOD") is a compound which was found for the first time by Fridovich, McCord, et al. J. Biol. Chem. 244, No. 22, 6049-6063 (1969) as an enzyme capable of converting superoxides, intermediates in oxidations by xanthine oxidase, in the course of their investigation on xanthine oxidase. It can be purified by a variety of methods, for example, heat treatment [Japanese Patent Publication Nos. 39832/1970 and 48721/1974; Sugiura, et al., J. Pharm. Dyn. 4, 235-244 (1981); etc.], salting-out with ammonium sulfate and precipitation in an organic solvent [Japanese Patent Laid-Open No. 155991/1982; Stephen, A. G, et al., Biochimica et Biophysica Acta, 289, 276-283 (1972)], gel filtration chromatography (Japanese Patent Laid-Open Nos. 102787/1981 and 10382/1982), affinity chromatography (Japanese Patent Laid-Open No. 121791/1983), etc. This SOD has drawn attention from the viewpoint of the oxygen toxicity protective mechanism in living bodies. It is now used as an anti-inflammatory for the treatment of chronic arthrorheumatic osteoarthritis, radiation-induced side effects, certain urosis and the like. Especially, bovine liver SOD is used clinically.
In the meantime, the sequence of amino acids in human erythrocyte Cu--Zn--SOD has been reported recently [Jabusch, et al., Biochemistry, 19, 2310-2316 (1980); and Barra, et al., FEBS Letters, 120, 53-55 (1980)]. There is also a report on the sequence of bases in a gene of human-origin SOD (hereinafter called "h-SOD") [Sherman, et al., Proc. Natl. Acad. Sci. U.S.A., 80, 5465-5469 (1983)]. Production of h-SOD in Escherichia coli (hereinafter called "E. coli) and yeast by a genetic operation has also been reported (Japanese Patent Laid-Open No. 137286/1985).
In order to use SOD clinically especially as an anti-inflammatory or for other therapeutic purposes, it is essential that physiologically-acceptable SOD is supplied stably. To permit in vivo application of SOD in human bodies, SOD is required, in view of predictable immunological problems, to be h-SOD or at least an h-SOD analogous polypeptide in an immunologically acceptable class and also to be a homogeneous enzyme. However, h-SOD has had a problem in its stable supply.